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README: add screencasts and examples.

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Roman Zeyde
2014-08-01 21:34:51 +03:00
parent 94c97d61ba
commit ecdc5e30df
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@@ -19,9 +19,9 @@ The modem is using OFDM over an audio cable with the following parameters:
- Sampling rate: 32 kHz
- BAUD rate: 1 kHz
- Symbol modulation: 64-QAM
- Carriers: (1,2,3,4,5,6,7,8,9) kHz
- Carriers: (1,2,3,4,5,6,7,8) kHz
This way, modem achieves 54kpbs bitrate = 6.75 kB/s.
This way, modem achieves 48kpbs bitrate = 6.0 kB/s.
A simple Reed-Solomon ECC is used, with (255,245) rate = ~3.9% overhead.
@@ -44,30 +44,90 @@ $ ./calib.py recv # run on the receiver side
```
The sender computer's audio level should be increased, until the received
**amplitude** is not higher than 0.5, while the **coherence** is 1.0 (so
**amplitude** is not higher than 0.5, while the **coherence** is 1.0 (so
saturation does not happen).
See http://youtu.be/iCg1tepGz10 for calibration demo.
## Testing
`test.sh` script is used to transmit a random data file between two computers
(using SSH connection) and to verify its correct reception.
See http://youtu.be/94yS3IZmtho for usage demo.
- Set connection parameters to sending computer:
- Prepare the sender:
```
$ export SRC_HOST="sender@tx.host"
$ export SRC_DIR="/home/sender/Code/amodem"
~/sender/amodem $ dd if=/dev/urandom of=data.send bs=125kB count=1 status=none
~/sender/amodem $ ./send.py <data.send >audio.pcm
2014-08-01 21:00:06,723 INFO Running MODEM @ 48.0 kbps
2014-08-01 21:00:06,773 INFO 3.210 seconds of training audio
2014-08-01 21:00:07,712 DEBUG 8.886 seconds of data audio
2014-08-01 21:00:08,714 DEBUG 14.941 seconds of data audio
2014-08-01 21:00:09,712 DEBUG 20.994 seconds of data audio
2014-08-01 21:00:10,381 INFO 21.846 seconds of data audio, for 125.000 kB of data
~/sender/amodem $ sha256sum data.send
008df57d4f3ed6e7a25d25afd57d04fc73140e8df604685bd34fcab58f5ddc01 data.send
```
- Set connection parameters to receiving computer:
- Start the receiver:
```
$ export DST_HOST="receiver@rx.host"
$ export SRC_DIR="/home/receiver/Code/amodem"
~/receiver/amodem $ ./wave.py record rx.int16 &
~/receiver/amodem $ ./recv.py <rx.int16 >data.recv
2014-08-01 21:00:30,068 INFO Running MODEM @ 48.0 kbps
2014-08-01 21:00:30,068 DEBUG Skipping first 0.100 seconds
```
- Run the test script:
- Start the sender:
```
~/sender/amodem $ ./wave.py play audio.pcm
```
- The receiver should print similar messages during demodulation:
```
$ ./test.sh
2014-08-01 21:00:34,847 INFO Carrier detected at ~4910.0 ms @ 1.0 kHz: coherence=99.991%, amplitude=0.485
2014-08-01 21:00:34,847 DEBUG Buffered 1000 ms of audio
2014-08-01 21:00:34,883 INFO Carrier starts at 4909.844 ms
2014-08-01 21:00:35,447 INFO Prefix OK
2014-08-01 21:00:35,656 DEBUG Current phase on carrier: 0.260
2014-08-01 21:00:35,656 DEBUG Excepted phase on carrier: 0.250
2014-08-01 21:00:35,657 INFO Frequency error: -13.24 ppm
2014-08-01 21:00:35,657 INFO Sampling error: 0.31 samples
2014-08-01 21:00:36,623 INFO 1.0 kHz: Noise sigma=0.0030, SNR=50.4 dB
2014-08-01 21:00:36,627 INFO 2.0 kHz: Noise sigma=0.0025, SNR=52.0 dB
2014-08-01 21:00:36,631 INFO 3.0 kHz: Noise sigma=0.0021, SNR=53.5 dB
2014-08-01 21:00:36,636 INFO 4.0 kHz: Noise sigma=0.0029, SNR=50.8 dB
2014-08-01 21:00:36,643 INFO 5.0 kHz: Noise sigma=0.0038, SNR=48.3 dB
2014-08-01 21:00:36,649 INFO 6.0 kHz: Noise sigma=0.0046, SNR=46.7 dB
2014-08-01 21:00:36,657 INFO 7.0 kHz: Noise sigma=0.0053, SNR=45.5 dB
2014-08-01 21:00:36,664 INFO 8.0 kHz: Noise sigma=0.0066, SNR=43.6 dB
2014-08-01 21:00:36,840 INFO Demodulation started
2014-08-01 21:00:37,591 DEBUG 6.0 kB, realtime: 75.04%, sampling error: +0.052%
2014-08-01 21:00:38,576 DEBUG 12.0 kB, realtime: 86.78%, sampling error: +0.069%
2014-08-01 21:00:39,522 DEBUG 18.0 kB, realtime: 89.38%, sampling error: +0.085%
2014-08-01 21:00:40,669 DEBUG 24.0 kB, realtime: 95.72%, sampling error: +0.085%
2014-08-01 21:00:41,510 DEBUG 30.0 kB, realtime: 93.39%, sampling error: +0.083%
2014-08-01 21:00:42,587 DEBUG 36.0 kB, realtime: 95.79%, sampling error: +0.082%
2014-08-01 21:00:43,586 DEBUG 42.0 kB, realtime: 96.37%, sampling error: +0.087%
2014-08-01 21:00:44,547 DEBUG 48.0 kB, realtime: 96.33%, sampling error: +0.064%
2014-08-01 21:00:45,594 DEBUG 54.0 kB, realtime: 97.27%, sampling error: +0.071%
2014-08-01 21:00:46,652 DEBUG 60.0 kB, realtime: 98.12%, sampling error: +0.056%
2014-08-01 21:00:47,600 DEBUG 66.0 kB, realtime: 97.81%, sampling error: +0.055%
2014-08-01 21:00:48,565 DEBUG 72.0 kB, realtime: 97.71%, sampling error: +0.038%
2014-08-01 21:00:49,618 DEBUG 78.0 kB, realtime: 98.29%, sampling error: +0.029%
2014-08-01 21:00:50,568 DEBUG 84.0 kB, realtime: 98.06%, sampling error: +0.019%
2014-08-01 21:00:51,645 DEBUG 90.0 kB, realtime: 98.70%, sampling error: +0.011%
2014-08-01 21:00:52,588 DEBUG 96.0 kB, realtime: 98.42%, sampling error: +0.002%
2014-08-01 21:00:53,600 DEBUG 102.0 kB, realtime: 98.59%, sampling error: -0.004%
2014-08-01 21:00:54,562 DEBUG 108.0 kB, realtime: 98.46%, sampling error: +0.006%
2014-08-01 21:00:55,541 DEBUG 114.0 kB, realtime: 98.43%, sampling error: -0.002%
2014-08-01 21:00:56,582 DEBUG 120.0 kB, realtime: 98.71%, sampling error: -0.006%
2014-08-01 21:00:57,545 DEBUG 126.0 kB, realtime: 98.60%, sampling error: -0.005%
2014-08-01 21:00:58,371 INFO EOF encountered
2014-08-01 21:00:58,371 DEBUG Demodulated 131.070 kB @ 21.531 seconds (98.6% realtime)
2014-08-01 21:00:58,372 INFO Received 125.000 kB @ 21.531 seconds = 5.806 kB/s
```
- Verify correctness:
```
~/receiver/amodem $ sha256sum data.recv
008df57d4f3ed6e7a25d25afd57d04fc73140e8df604685bd34fcab58f5ddc01 data.recv
```